In the manufacture of a semiconductor device, various kinds of heat treatments such as oxidization, diffusion, CVD and annealing are performed with respect to a target object to be processed, e.g., a semiconductor wafer. An example of a heat treatment apparatus for performing these processes is a vertical heat treatment apparatus capable of performing concurrent heat treatment on multiple wafers.
In general, a vertical heat treatment apparatus includes a lid body vertically movable to open and close a furnace opening for a reaction tube of a heat treatment furnace. A heat treatment boat for supporting a plurality of wafers at multiple stories along an up-down direction is installed on the lid body. The heat treatment boat is supported by a leg which is rotated by a rotating shaft extending through the lid body.
An inert gas is supplied to a space between the leg and the lid body in order to prevent a process gas from moving toward a side of the rotating shaft from the space between the leg and the lid body.
In some vertical heat treatment apparatuses, an inert gas is supplied to a gap between the leg of the heat treatment boat and the lid body and discharged into the heat treatment furnace. However, it is difficult to adjust the gap between the leg of the heat treatment boat and the lid body. Sometimes, the inert gas cannot be sufficiently and reliably discharged from the gap between the leg and the lid body into the reaction tube.
More specifically, a horizontal purge flow path is formed by a seat member for the leg and a lid body. In this case, the purge flow path is formed as a gap of 0.2 to 0.5 mm in height by a pull screw and a push screw. A collapse of balance due to the repeated thermal expansion and contraction of the screws or the degradation over time may occur. Such a collapse may disrupt the gap from maintaining the predetermined distance, and there may be a problem that the seat member and the lid body come in contact with each other to generate unwanted particles. Moreover, if a N2 purge flow rate is reduced when the size of the gap is not large enough to serve as the purge flow path, a problem occurs in that a cleaning gas is reversely diffused, thereby corroding a hub of the rotating shaft.